Applicants have, for a number of years, been associated with production of an airborne sonar system in which a sonar transducer of substantial weight is carried in a helicopter and periodically lowered into and raised from the water at the end of a cable by means of a hoist mechanism driving the cable. The cable used typically has a substantial number of individual conducting wires (or small bundles of wires) as well as a wire rope strength member carried at its center. The hoist mechanism is driven in such manner as to cause the transducer to be lowered into the water or returned to the helicopter, thereby coiling the cable onto its reel. The inner end of the cable is terminated at an electrical connector which is fixedly secured to the reel. In a preferred arrangement the cable passes through an opening in the cylindrical spool surface of the reel, and the connector is fastened to a support on the interior of the said spool surface. As the cable leaves the reel it is caused to pass over a pair of sheaves and past a cable angle sensor which makes contact with the cable and which is attached to the hoist mechanism such that it provides a signal indicating the angle of descent of the cable relative to the attitude of the helicopter.
For various reasons the cable may separate from the reel. It may happen because of a malfunction in the operation of the hoist mechanism or because of errors in judgement of the hoist operator. It may happen intentionally because of operating difficulties with the helicopter or because of threatened imminent hostile action whereby the helicopter pilot needs to jettison the cable and transducer quickly. For whatever reason separation occurs, it should occur at a limited and predictable force, and when it occurs the cable should pull clean from the connector so that there is not a substantial ball or chunk of potting compound or other material of significantly greater diameter than the cable adhering to the cable to be pulled through or past the sheaves and the cable angle sensor. Such a larger diameter protuberance can cause substantial damage to the hoist mechanism including the sheaves as well as to the cable angle sensor. (There is also a possibility that such a protuberance could become lodged or wedged in the hoist mechanism, leaving the length of cable and the transducer still connected to the helicopter.) It therefore becomes of great importance that the connection of the cable to the connector at the reel be such that the cable will always pull away clean from the connector .